Recent epidemiologic studies suggest that the acute respiratory distress syndrome (ARDS) is more common than previously reported and has an overall mortality of 40%. Patients who survive the initial stages of acute lung injury (ALI) often develop fibroproliferative changes in the lungs that place them at higher risk for adverse clinical outcomes. In accordance with the mission of the NHLBI to improve the care of patients with lung disease, this proposal will examine the mechanisms of lung fibrosis after ALI. Previous studies from our laboratory group showed that activation of the Fas-pathway plays an important role in the development of both acute lung injury and fibroproliferation. Although the precise mechanisms that underlie these events are largely unknown, our previous work suggests that early epithelial apoptosis as well as the release of key pro-fibrotic mediators, such as MMP-12, from the alveolar macrophages are important. These studies also highlighted the fact that the development of lung fibrosis is complex and results from the interaction of multiple different proteins and biologic pathways. Traditional experimental methods that explore single biologic pathways are limited in their ability to study these interactions. Our laboratory uses systems-based methodologies, such as proteomics, to overcome these limitations. Thus, the overall objective of this proposal is to study the mechanisms of Fas-induced pulmonary fibrosis using a systems-based proteomics approach. We will use chimeric mice that have Fas on their myeloid or non-myeloid cells to study the relative contribution of the alveolar epithelium and alveolar macrophages in Fas-induced lung fibrosis. In addition, we will perform proteomic analysis on the bronchoalveolar lavage fluid of the chimeric mice to identify the proteins that are expressed in the airspaces when Fas-activates each of these cell types, and to determine the key proteins that are associated with Fas-induced lung fibrosis. Finally, we will use proteomic analysis to examine how these pro-fibrotic proteins are modified by MMP-12. Acute lung injury and its most severe manifestation, the acute respiratory distress syndrome (ARDS), are common causes of morbidity and mortality in critically-ill patients. The studies in this proposal will attempt to define the key proteins and protein pathways that are expressed when the lungs develop fibrosis after acute lung injury. Defining these key mediators to will be an important step to finding new interventions to treat this devastating illness. [unreadable] [unreadable] [unreadable]